Comparison between high-speed video recordings of lightning and the detections of the Catalan Lightning Location Network (XDDE)

Lightning detections of the Catalan Lightning Location Network (XDDE) are compared with high speed video recordings carried out in Spain during summer 2009. At that time the XDDE was composed by four sensors: two SAFIR 3000 type and two LS8000 type. The comparison showed good agreement in the observations at the center and at the south of the network. However, the observations recorded at the north of the network showed a poorer detection efficiency and location accuracy. On the other hand, the fine comparison between frame by frame of video recordings and network detections reveals that the network often detects mostly intra-cloud (IC) sources which probably belong to the preliminary breakdown in downward cloud-to-ground flashes. In some cases few sources are detected during steeped leaders toward to the ground. In the case of our observed IC flashes, the detected sources never corresponded to observations of propagation leaders, if not, small burst of detections were linked to permanent illuminated channels or permanent visible luminosity from the cloud.Postprint (published version

X-rays and microwave RF power from high voltage laboratory sparks

Lightning flashes involve high energy processes that still are not well understood. In the laboratory, high voltage pulses are used to produce long sparks in open air allowing the production of energetic radiation. In this paper X-rays emitted by long sparks in air are simultaneously measured with the RF power radiation at 2.4 GHz. The experiment showed that the measured RF power systematically peaks at the time of the X-rays generation (in the microsecond time scale). All of the triggered sparks present peaks of RF radiation before the breakdown of the gap. The RF peaks are related to the applied voltage to the gap. RF peaks are also detected in discharges without breakdown. Cases where X-rays are detected presented higher RF power. The results indicate that at some stage of the discharge, before the breakdown, electrons are very fast accelerated letting in some cases to produce X-rays. Microwave radiation and X-rays may come from the same process.Preprin

High-speed video recordings of lightning, electric fields and high-energy detections during thunderstorms in Catalonia Spain

High-speed video recordings of natural lightning flashes show amazing details of this phenomenon. The paper summarizes the results of the 2009 measurement campaign where the combination of electric fields, total lightning, high-energy detections and high-speed videos provided a valuable data. The paper describes the visible differences between the recorded negative, positive and upward cloudto- ground flashes. Thanks to the precise time synchronization of each video frame we investigated which processes are detected by the lightning location networks (VHF and VLF). We suggest that the VHF interferometer network detects mostly those processes of intra-cloud flashes where substantial charge is transferred during few milliseconds. The study of the detections of intra-cloud events provided by the VLF network were related to high and fast (less than a millisecond) charge transfers within the cloud that saturated the camera in the same manner as return strokes in cloud-to-ground flashes. In other hand, the paper discusses the high-energy detections related to a very close cloud-to-ground lightning flash.Preprin

Winter lightning activity in specific global regions and implications to wind turbines and tall structures

The paper presents winter lightning maps on specific regions in the northern hemisphere. Four different degrees of winter lightning activity are defined based on information derived from Japanese case. Based on this reference case it is possible to determine regions where winter lightning can be a threat to specific structures. Guidance on risk assessment to tall structures and wind turbines are described as well.Preprin

Registration of X-rays at 2500 m altitude in association with lightning flashes and thunderstorms

Electric fields and high-energy radiation of natural lightning measured at close range from a mountaintop tower are discussed. In none of the 12 negative cloud-to-ground upward flashes were X-rays observed. Also no energetic radiation was found in one negative upward leader at close range (20¿m). In the first of two consecutive negative cloud-to-ground flashes, X-rays were detected during the last ~1.75¿ms of the leader. During the time of energetic radiation in the flash an intense burst of intracloud VHF sources was located by the interferometers. The X-ray production is attributed to the high electric field runaway electron mechanism during leader stepping. Even though the second flash struck closer than the previous one, no X-rays were detected. The absence of energetic radiation is attributed to being outside of the beam of X-ray photons from the leader tip or to the stepping process not allowing sufficiently intense electric fields ahead of the leader tip. High-speed video of downward negative leaders at the time when X-rays are commonly detected on the ground revealed the increase of speed and luminosity of the leader. Both phenomena allow higher electric fields at the leader front favoring energetic radiation. Background radiation was also measured during thunderstorms. The count rate of a particular day is presented and discussed. The increases in the radiation count rate are more coincident with radar reflectivity levels above ~30 dBZ than with the total lightning activity close to the site. The increases of dose are attributed to radon daughter-ion precipitationPostprint (published version

High-speed observations of transient luminous events and lightning (The 2008/2009 Ebro Valley campaign)

Preprin

Global distribution of winter lightning: a threat to wind turbines and aircraft

Lightning is one of the major threats to multi-megawatt wind turbines and a concern for modern aircraft due to the use of lightweight composite materials. Both wind turbines and aircraft can initiate lightning, and very favorable conditions for lightning initiation occur in winter thunderstorms. Moreover, winter thunderstorms are characterized by a relatively high production of very energetic lightning. This paper reviews the different types of lightning interactions and summarizes the well-known winter thunderstorm areas. Until now comprehensive maps of global distribution of winter lightning prevalence to be used for risk assessment have been unavailable. In this paper we present the global winter lightning activity for a period of 5 years. Using lightning location data and meteorological re-analysis data, six maps are created: annual winter lightning stroke density, seasonal variation of the winter lightning and the annual number of winter thunderstorm days. In the Northern Hemisphere, the maps confirmed Japan to be one of the most active regions but other areas such as the Mediterranean and the USA are active as well. In the Southern Hemisphere, Uruguay and surrounding area, the southwestern Indian Ocean and the Tasman Sea experience the highest activity. The maps provided here can be used in the development of a risk assessment.Peer ReviewedPostprint (published version

Basic lightning flash properties derived from lightning mapping array data

The size and duration of lightning flashes are examined. Data from the Ebro Valley Laboratory Lightning Mapping Array is used as reference. Additional data from the VLF/LF LINET network is included. In the analysis, each flash is simplified by a confidence ellipse fitting most of the detected sources. The major axis of the ellipse is adopted as the flash length. Flash durations are computed too. The analysis of 778 flashes results in a median flash length of ¿14 km with a median duration of ¿0.3 s. The results presented, besides characterizing the storm activity, they can be useful to define stroke grouping criteria, lightning flash density calculations and lightning warning purposes.Postprint (published version

Potential use of space-based lightning detection in electric power systems

Information about lightning activity and its parameters is necessary to design and evaluate the lightning protection of an electrical power system. This information can be obtained from ground-based lightning detection networks that provide information on cloud-to-ground lightning strikes with a location accuracy of few hundred meters. Recently, the first satellite-based lightning optical detectors are operating continuously from geostationary orbits. These imagers observe the luminosity escaping from clouds to detect and locate total lightning activity with a spatial accuracy of several kilometers. This allows delineating the initiation and propagation (sometimes over tens to hundreds of kilometers before striking the ground) not observable by the ground-based networks. In this paper, we explore the use of this new technology for lightning protection in power systems. We focus on tall objects such as wind turbines and overhead transmission lines. We show how the optical detections allow identifying lightning flashes that likely produce continuing currents. This provides additional information for the identification of dangerous events and also can be used to estimate the number of upward-flashes from tall objects triggered by a nearby flash. The analysis of a transmission line shows the concentration of faults in the areas of high total lightning flash density. We found regional variations of the optical energy of the flashes along the line.This work was supported by research grants ESP2017-86263-C4-2-R funded by MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”, by the “European Union”; and Grants PID2019- 109269RB-C42 and ENE2017-91636-EXP funded by MCIN/AEI/ 10.13039/501100011033. S. Goodman was in part supported by NASA Grant 80NSSC18K1689. M. M. F. Saba was in part supported by research grants 2012/15375–7 and 2013/05784–0, from Sao ˜ Paulo Research Foundation (FAPESP). S. Visacro was supported by a research grant (307381/2019–6) of the Brazilian National Council of Technological and Scientific Development (CNPq). The GLM data are available from the NOAA National Centers for Environmental Information (NCEI) and Cloud Service Providers (e.g., Amazon Web Services, AWS). The LIS data are available from the NASA GHRC Distributed Active Archive Center (DAAC) (https:// https://ghrc.nsstc.nasa.gov/home/access-data. The power system information for the 500 kV transmission line is provided by ISA-INTERCOLOMBIA and is supported by L. Porras.Peer ReviewedPostprint (author's final draft